In recent years, in welding industry, in order to improve productivity, the need for improving the quality of welding has been increased. Especially, reduction of spatters at the start of an arc has been required. At the start of an arc, since it takes a long time to form a molten pool on a base material, it takes a long time for the arc to be stabilized, so that it is more likely that generation of spatters increases and the spatters adhere to the base material. Therefore, aftertreatment for removing the adhering spatters is needed, and the welding productivity may be reduced. Furthermore, if a product is distributed in a state in which spatters adhere to a base material without carrying out aftertreatment, the product value may be remarkably damaged.
As a conventional arc start control, it is known that at least one pulse wave-like electric current is supplied by pulse control at the start of an arc, a molten pool to be firstly formed on the base material is formed by separation and shift, and, after the pulse wave-like electric current is supplied, pulse control is changed from pulse control to short-circuit control. In such a conventional arc start control, a torch for feeding a wire as an electrode is mounted on the tip end of an arm of an arc-welding robot, and starting control is carried out at the lift-up starting time for lifting up the arm tip at the start of an arc. In a state in which a molten pool is not formed on the base material at the early stage of the arc start, with the aim of separating and shifting a droplet from the tip end of the wire to form a molten pool, a pulse wave-like current is output so as to reduce the generation of spatters (see, for example, Patent Document 1).
FIG. 4 shows a schematic configuration of a conventional arc welding apparatus. In FIG. 4, primary-side rectifying element 3 rectifies an output of input power source 1 and outputs the rectified output. Switching element 4 converts a direct current output from primary rectifying element 3 into an alternating current so as to control a welding output. Main transformer 2 transforms the alternating current output of switching element 4. An output of main transformer 2 is output as a welding output via secondary-side rectifying element 6 for rectifying the secondary-side output of main transformer 2 and reactor 5.
Setting section 35 sets and outputs various parameters such as magnitude of a pulse current and a pulse time based on the setting conditions such as a set current, a set voltage, an amount of fed wire, types of shielding gases, types of wires, a wire diameter, and a welding method, which are input from an input unit (not shown) and the like. Setting section 35 includes a storage section (not shown) for storing table or formula for determining the above-mentioned parameters and a calculation section (not shown) for carrying out calculation and the like, with which parameters are set.
Welding voltage detector 9 detects a welding voltage, and welding current detector 8 detects a welding current. Pulse welding control unit 37 receives inputs of an output of welding current detector 8, an output of welding voltage detector 9 and an output of setting section 35, and outputs a command to control pulse welding. Pulse welding control unit 37, as mentioned below, controls to allow a pulse-like current to flow for a predetermined time after an arc start current for generating an arc flows. Short-circuit welding control unit 36 receives inputs of an output of welding current detector 8, an output of welding voltage detector 9 and an output of setting section 35, and outputs a command to carry out control. Pulse welding control unit 37 and short-circuit welding control unit 36 have, for example, a function of comparing respective output signals from welding current detector 8 and welding voltage detector 9 with parameter values (command values) and controlling a welding current and a welding voltage to coincide with the parameter values, so that the welding current and welding voltage correspond to the parameter values (command value) input from setting section 35.
Changing section 38 receives an input of the output of setting section 35, and outputs a timing of changing from pulse welding control to short-circuit welding control to driving section 34. Changing section 38 has a timer function and can count a time until a predetermined time has passed from a time point at which an output of setting section 35 is input. Driving section 34 has a function of receiving an input of the output of short-circuit welding control unit 36, the output of pulse welding control unit 37 and the output of changing section 38, and changing between outputting the output of short-circuit welding control unit 36 to switching element 4 and outputting the output of pulse welding control unit 37 to switching element 4 according to the output of changing section 38.
A control method of the arc start by a conventional arc welding apparatus configured as mentioned above is described with reference to drawings.
FIG. 5 shows examples of waveforms of a wire feed speed, a welding voltage and a welding current at the time of welding of consumable electrode arc welding. FIG. 5 shows an example of a waveform in which the start of welding is instructed at time point 200, an arcing current flows and arc is generated at time point 201, then pulse wave-like welding current Aw flows twice by pulse welding control, and the control state is then changed to the short-circuit welding control at time point 202.
At time point 201 as a time point at which an arc is generated, driving section 34 outputs the output of pulse welding control unit 37 to switching element 4 based on the input from changing section 38. Furthermore, changing section 38 counts an elapsed time from time point 201 at which welding current Aw is detected. Thereafter, at time point 202 at which a predetermined time has passed, to change welding control from the pulse welding control to the short-circuit welding control, driving section 34 controls the output of short-circuit welding control 36 to be output to switching element 4.
With this control, during interval 203 from time point 201 as a time starting point at which an arc is generated to time point 202 as a changing time point, pulse control is carried out based on the output of pulse welding control unit 37, and a droplet at the tip end of a welding wire (not shown) is separated and shifted to a base material (not shown). Thereafter, at time point 202 as a changing time point after a predetermined time has passed from time point 201 as an arc generating time point, changing section 38 sends a change instruction to driving section 34, and thereby the output of short-circuit control unit 36 is output to switching element 4, and the welding output control is changed from the pulse welding control to the short-circuit welding control. Thereafter, during interval 204 after changing time point 202, short-circuit control is carried out by short-circuit welding control unit 36.
As mentioned above, in conventional arc start control method and arc welding apparatus, after an arc start current flows, at least one pulse wave-like current is supplied by pulse control, and a molten pool firstly formed on a base material can be formed by separation and shift. Thus, a droplet on the wire tip end can be shifted to be short-circuited smoothly, and generation of spatters and adhesion of spatters can be reduced during the time after an arc is generated before the arc is stabilized.
Furthermore, by combining the above-mentioned arc welding machine and an arc welding robot and mounting a welding wire as an electrode on the tip end of the arm of the arc welding robot, the above-mentioned arc start control may be carried out when the lift-up starting is executed in which the tip end of the arm is lifted up at the arc starting time. When lift-up is carried out at time point 201 as an arc generating time point, the welding wire is prevented from being melted to generate spatters in a short-circuit state, and spatters are reduced at time point 201 as an arc generating time point. Furthermore, the lift-up makes it possible to obtain the distance between the wire tip end and the base material instantaneously. That is to say, since it is possible to instantaneously obtain a distance that is larger than the size of a droplet at the pulse controlling time, short-circuit does not occur, and separation and shift can be carried out smoothly. Thus, generation and adhesion of spatters can be further reduced.
In this way, output control in a conventional arc welding machine has an effect of reducing the amount of spatters generated at the start of an arc by separating and shifting a droplet from the tip end of the wire by pulse welding control and forming a molten pool on the base material.
The shift of a droplet when a molten pool is formed is described with reference to drawings. In the shift of a droplet when a molten pool is formed, as shown in, for example, FIG. 6 (the upper part shows a state of shifting a droplet, and the lower part shows a welding current (A)), since arc 52 is generated from the entire part of molten pool 51 on base material 50, arc 52 is spread and covers a wide range of the lower part of droplet 53a at the tip end of wire 53. Therefore, since the current density is low and an electromagnetic pinch force by peak current 55 of pulse current 54 is large, the effect of pushing up the droplet is reduced, and the droplet is smoothly separated and shifted to molten pool 51 from the tip end of wire 53. Note here that wire 53 is fed in a state in which it is held by chip 56.
However, as shown in, for example, FIG. 7 (the upper part shows a state of shifting a droplet, and the lower part shows a welding current (A)), since a portion in which an arc is generated in the early stage of the arc start does not have a molten pool on base material 50, arc 52 is concentrated in a thin portion, a current density of the lower part of droplet 53a at the tip end of wire 53 becomes higher, and a force for pushing up droplet 53a works. Since this push-up force may become larger than the electromagnetic pinch force in many cases, large droplet 53a does not shift in the direction of base material 50, but it is pushed up in a direction different from that of base material 50. Therefore, when droplet 53a is separated from the tip end of wire 53, as shown in FIG. 7, some droplets 53a may scatter as spatters 53b. If spatters 53b are scattered, they may adhere to base material 50 and may not be able to be detached. In other words, the amount of spatters 53b to be generated can be reduced also in conventional control, but spatters 53b that may be generated by the above-mentioned push-up force are not sufficiently handled, so that large size of spatters 53b may be generated and adhere to base material 50.
The present invention provides an arc start control method and an arc welding apparatus for reducing an amount of spatters generated from a time when an arc is generated to a time when the arc is stabilized.